The present invention relates to a method and apparatus for controlling periodic flashing of vehicle directional lamps and particularly to an improvement in the generation of pulses which control the periodic flashing of the directional lamps.
It is known well in the direction indicating system of an automotive vehicle that a group of front, rear and side directional lamps are energized in response to a train of periodic pulses to flash periodically upon requirement for the indication of vehicle turning direction. It is also known that the frequency of the periodic pulses is increased upon disconnection of the front or rear directional lamp to increase flashing frequency of the remaining directional lamps.
One of this system is disclosed in the prior art, U.S. Pat. No. 3,858,177 issued on Dec. 31, 1974, in which front and rear directional lamps are connected in parallel with each other and connected in series with a battery, a current detecting resistor, a relay and a selection switch and an electronic circuit is provided to generate a train of periodic pulses applied to the relay. The electronic circuit is connected to the selection switch so that the periodic pulses are generated only during closure of the selection switch.
According to this kind of electric connection between the electronic circuit and the selection switch, the electronic circuit is likely to erroneously generate the pulses. This erroneous operation of the electronic circuit results from noise signal which are induced on long electric wirings between the selection switch and the directional lamps in a vehicle wiring connection. It should be noticed further that the electronic circuit, when integrated into a single semiconductor chip, is broken down by the noise signals.